USE OF MULTIPLE PRIMARY CANCERS TO INDICATE ASSOCIATIONS BETWEEN SMOKING AND CANCER INCIDENCE - AN ANALYSIS OF 500,000 CANCER CASES DIAGNOSED IN NORWAY DURING 1953-93

The occurrence of multiple primary cancers is relatively rare, but may provide indications of common or opposite risk factors for different types of cancer. In the present study, the occurrence of multiple prim ary cancers was used to indicate possible associations between smoking and the incidence of cancers other than those generally accepted as s moking-associated. All cancer cases in persons above the age of 30, re gistered at the population-based Cancer Registry of Norway (1953-1993) , were used in the analysis, For each type of cancer, the observed occ urrence of smoking-associated cancers in the patients was compared wit h the expected occurrence if the patients had the same risk as the gen eral population. Similar comparisons were made for the occurrence of o ther cancers in patients with a smoking-associated cancer. The results were presented as standardized incidence ratio (SIR), the ratio of th e observed and the expected numbers of cases. The results indicated th at uterine cervical cancer may share some important risk factor(s) wit h the cancers generally accepted as smoking-associated, This is in acc ordance with the literature, where an association between smoking and uterine cervical cancer has been found consistently. In addition, the results for liver cancer and leukemia indicated that these types of ca ncer also share some risk factor(s) with the smoking-associated cancer s. (C) 1997 Wiley-Liss, Inc.